1. Field of the Invention
The present invention relates to a substrate processing method, and more specifically, to a substrate processing method to process a substrate including at least a process layer, an intermediate layer, and a mask layer which are stacked in this order.
2. Description of the Related Art
As a conventional wafer for a semiconductor device, there is a wafer including an oxide film including an impurity (such as a TEOS (Tetra Ethyl Ortho Silicate) film), which is formed by a CVD process or the like, a conductive film (such as a TiN film), a reflection preventive film (BARC film), and a photoresist film which are stacked in this order over a silicon substrate by a CVD process or the like (for example, see Patent Document 1). A photoresist film is formed in a predetermined pattern by photolithography to serve as a mask when etching the reflection preventive film and the conductive film.
In recent years, as semiconductor devices are further downsized, there is a growing demand for forming more minute circuit patterns over the wafer as described above. To form such minute circuit patterns, small size apertures (via holes or trenches) are required to be formed in a film for use in etching, by scaling down the minimum size of a pattern formed in a photoresist film when manufacturing the semiconductor device.    [Patent Document 1] Japanese Patent Application Publication No. 2006-190939
The minimum size of a pattern formed in a photoresist film is defined by the minimum possible size realized by photolithography. However, due to variations of focal distance or the like, there is a limit in the minimum possible size developed by photolithography. For example, the minimum possible size developed by photolithography is 80 nm, although a process size of about 30 nm is required to satisfy the demand for downsizing the semiconductor devices.
Therefore, it was conventionally impossible to form apertures in a film to be etched, which have a size to satisfy the demand for downsizing the semiconductor devices.